1. Field of the Invention
The present invention relates to wind machines of the panemone type and namely, a vertical axis wind collector capable of reacting to horizontal winds from any direction.
2. Description of the Prior Art
Propeller type windmills of large capacity and relatively high speed capability have either required massive towers to resist the horizontal thrust, or incorporation of a braking device to stop the windmill or a vane feathering device to reduce its effectiveness during strong wind conditions.
A large propeller turning at high speed generates a substantial gyroscopic force which will resist the directional changes required by shifts in wind direction. It is well known by those who now harness wind energy that a frequent condition involves a wind of about twenty knots speed blowing from a relatively narrow compass vector, but accompanied by recurrent gusts at considerably higher speeds which strike the windmill at a significantly different angle. As a result the supporting tower may be subjected to a dangerously severe twising action.
It has been recognized that vertical-axis rotors have the major advantage over horizontal-axis rotors that they do not have to be turned into the wind as the direction of the windstream varies. A review of prior art panemones is given on pages 22-25 of "Wind Machines" published by the U.S. Government Printing Office in 1976 (0-204-143) for the National Science Foundation (NSF-RA-N-75-051). As indicated in that publication, various types of vertical-axis panemones have been developed in the past that use drag forces to turn rotors of different shapes. These include those panemones that use plates, cups, or turbines as the drag device, and the Savonius S-shaped cross-section rotors which provide some lift force but are still predominantly drag devices. Such devices have relatively high starting torques, compared to lift devices, but relatively low tip-to-wind speeds and low power outputs per given rotor size, weight and cost.
The aforesaid publication also indicates that in the past few years attention has been directed to the Darrieus-type rotor invented in the 1920's by G. J. M. Darrieus of France. Those rotors are characterized by curved blades with airfoil cross sections, and are said to have relatively low starting torques, but relatively high power outputs per given rotor weight and cost.